1. Technical Field of the Invention
The present invention relates to a sliding material excellent in friction and wear characteristics and a method of manufacturing the same.
The term "sliding material" as used herein is to be understood as a construction including plain bearing or bearing material or self-lubricating material which is suitable for use as antifriction material for producing sliding members, such as bearing bushes, shoes, slide plates, and sliding members used in clutches, brakes, etc., and collectors.
The term "plain bearing or bearing material or self-lubricating material" is to be understood as including a steel backing to which is bonded a layer of porous bronze constituting a matrix in which the porous bronze at least at and adjacent to its exposed surface is impregnated with a mixture of PTFE and lead etc.
2. Prior Art
Conventional sliding materials and methods of manufacturing the same are disclosed, for example, in the following Japanese Patent Kokoku (Post Exam. Publications) and Japanese Patent Application Kokai (Laid-Open) (1), (2),. and (3). The gist thereof lies in a sliding material comprising a backing metal having a porous metal layer formed on the surface thereof in which pores are defined and compositions for impregnation coating are shown below in (1), (2), and (3) impregnated and coated to the pores and the surface thereof.
(1) Japanese Patent Kokoku No. 39-16950 (using, e.g., PTFE-20Pb or PTFE-20PbO in a volume percent as a composition for impregnation coating) (PTFE: polytetrafluoroethylene)
(2) Japanese Patent Kokoku No. 61-52322 (using, e.g., PTFE-20PFA in a volume percent as a composition for impregnation coating) (PFA: tetrafluoroethylene-perfluoroalkylvinylether copolymer)
(3) Japanese Patent Kokai No. 59-103022 (using, e.g., PTFE-10PFA-20Pb in a volume percent as a composition for impregnation coating)
Here, attention must be paid to Japanese Patent Kokai (1) above which discloses coarse lead powder having a mesh of 300 B.S.S as the type of metal lead used as shown in the example on lines 21 and 22 of the right column of page 1. The lead powder has a ratio of surface area to weight of 500 cm.sup.2 /g, and it is found that lead powder having a very small relative surface area was used. Further, the lead powder used above in (2) and (3) was substantially similar to that used in (1) above, in consideration of the technical level at that time. In addition, the above prior arts (2) and (3) used various kinds of meltable fluorocarbon resins.
A sliding material and a method of manufacturing the same according to the technologies as disclosed in prior arts (1), (2), and (3) in which the very coarse lead powder, i.e., the lead powder having a very small relative surface area and various kinds of meltable fluorocarbon resins used do not satisfy both friction and wear characteristics when the sliding material is slid in a dry state and wear and cavitation proofing characteristics when it is slid under the boundary lubrication or semi-dry lubrication is not satisfactory.
A problem to be solved by the present invention is to determine a size of metal lead and to select a specific fluorocarbon resin to satisfy both of the above characteristics.